So I just recently got a E4200v1 with the intention to of using it to monitor and throttle usage of my network. Monitoring of usage is working wonderfully utilizing an attached usb drive for bw/iptraffic storage. However, enabling BW Limiting on even one client is causing the router to repeatedly crash until disabled. Is this a known issue, and are there any logs I should post to assist in this getting fixed?

Yes, BW limiter and other modules (Nocat, CTF) crash in the actual status of source code, we are working to establish a more 'clean' iptables rules. Unfortunately the code in Tomato began corrupted by many modifications without enough 'test'. I'll post when solved, we are on the way.
These issues appear very random in routers with low RAM (in comparison with tanks like Asus RT's).. like E3000, 4200 and also when VLAN feature splitted the nvram area for the 6 ports …
To stop rebooting and at least disable the feature provoking the issue disconnect WAN cable, then you can access the GUI and deactivate the 'reboot feature'.